Low-temperature carbonization of coal



Dec. 16, 1952 c. E. LESHER 2,622,059

LOW-TEMPERATURE CARBONIZATION OF COAL Filed Feb. 2a, 1948 2 SHEETS-SHEET1 a/x A INVENTOR CARL E. LESHER ATTORNEY Dec. 15, 1952 c. E. LESHER2,622,059

LOW-TEMPERATURE CARBONIZATION OF COAL Filed Feb. 28, 1948 2 SHEETS-SHEET2 3 I00 98 I 94 M, 9 84 o we 6 l5 2,6 /'o8' l6 8 l8 a7 I9 mg L Hgurz 3INVENTOR CARL E. LE SH/ER J). I F e ZTTQRNEY Patented Dec. 16, 1952LOW-TEMPERATURE CARBONIZATION OF COAL Carl E. Lesher, Ben Avon Heights,Pa., assignor to Pittsburgh Consolidation Goal 1 Company, Pittsburgh,Pa., a corporation of'Pe'nnsylvania Application February 28, 1948,Serial No. 11,964

4 Claims.

This invention relates to the distillation of carbonaceous materialsand, more particularly, to the distillation of distillable carbonaceoussolids such as bituminous coal, lignite and oil. shale.

The primary object of the present invention is to provide a process andan apparatus for continuously distilling carbonaceous solids.

Another object of the present invention is to provide a process and anapparatus for the distillation of carbonaceous solids to continuouslyproduce a solid product and a maximum yield of volatile products at ahigh throughput rate of carbonaceous solids.

A further object of the present invention is to provide a process andapparatus for continuously producing from distillable bituminous coalsor lignites a granular carbonaceous product within the approximate sizerange of the coal or lignite charge and substantially free of lumps ofcoke.

- In accordance with my invention, the above objects are attained by theuse of a two vessel system. One vessel serves as a preheating zone forraising the temperature of finely divided previously distilledcarbonaceous material to a temperature sufficiently high to distill thematerial being treated. The second vessel is the distillation zone andcomprises a substantially cylindrical horizontal retort which is mountedfor rotation aboutits central longitudinal axis.

In operation, hot distillation residue from the I heatin zone and finelydivided undistilled carbonaceous solids areseparately chargedinto oneend of the rotating retort in such proportions that the averagetemperature of the solids in the retort .'is' within the. distillationrange of the car- P."

bonaceous solids. The rotation of the retort produces intimate mixing ofthe hot distillation residue and distillable solids whereby distillationof the latter takes place. Solid distillation residue is continuouslyremoved from the opposite and outlet end of the retort, thereby causingprogressive and continuous movement of solids through'the retort. Thevolatile products are also continuously removed through the same outletend of the retort. To complete the cycle a In the preferred embodimentof this invention, thepreheating zone, as distinguished from: thedistillation. zone, comprises a-fluid iz ed, bed of granulardistillation residue with the fluid condition being maintained by oxygenor an oxygen bearing gas. The entire bed of granular car.- bonaceoussolids is thereby uniformly raised to the desired'temperature bycombustion of a part thereof. I have found that the granulardistillation residue produced in the rotating retort is eminentlyadapted to being fluidized. The'us e of the fluidized bed to effectheating'of the distillation residue-in combination with distillation ofthe distillable carbonaceous solids by direct contact with the hotdlstillationvresidue results in the maximumutilization of heat in thesystem.

The operation of the above two vessel system on bituminous solids suchas high volatile Pittsburgh seam coal which is acoking coaLproducescontinuously a high yield of liquid tarrich in tar acids, a substantialquantity of high B. t. u. gas, and. a granular loose char which issuitable for a number of usesincluding that as solid boiler fuel.Furthermore, the production capacity of the system has been found toconsiderably exceed expectations and to be greatly superior to anyheretofore proposed to the best or my knowledge.

Other details, objects and advantages of the invention will becomeapparent upon reference to the following description of a preferredembodiment thereof.

In the accompanying drawings I have shown apparatus by the use of whichthe invention may be practiced and have illustrated a. present preferredmethod of practicing the invention, in which:

,Figure 1 is a diagrammatic showing of the apparatus in which theinvention may be practiced; I

Figure 2 is a centrallongitudinal cross-seetional view of'a portion ofthe apparatus illustrated in Figure l;

Figure 3 is a vertical transverse cross-sectional view taken on the line33 of Figure 2.

Referring to Figure 1 of the drawings, a flow sheet of a preferredembodiment of the invention is shown. Numeral l0 designates asubstantially cylindrical horizontal retort which is mounted forrotation about its central longitudinal axis. This retort is providedwith a layer of insulating material ii. A. hopper 14 serves to holddistillable carbonaceous solids which are conveyed to the interiorof theretort Ill through a conduit l5 by means of a variable screw feeder l 6.Another variable screw feeder I8 located adjacent to feeder i6 isadapted to introduce hot carbonaceous distillation residue in granularform through a conduit IS into the retort wherein a bed 28 of solids ofsubstantially constant level is maintained by means of lifters 22 and24. The latter upon rotation of the retort l0 pick up solids from thebed 20 and drop them into a hopper 26 from which the solids are.conveyed out of the retort through a conduit 21 by means of a screwfeeder 28. A more detailed description of the retort 10 will be givenlater in connection with Figures 2 and 3.

The volatile products produced within the retort l0 leave the retortthrough the conduit 21 and are conducted to a dust chamber 30 which isprovided with water 32 for the collection of dust. From this chamber thegas is carriedthrough conduit 34 to a spray scrubber 36 where condensation of any condensable vapors takes place. Liquid condensate is removedthrough the bottom 38 of the scrubber while the non-condensable gasproduct leaves the scrubber at the top through conduit 40.

The solid products from the rotating retort ID are prevented fromentering the dust chamber 30 by means of a guard 42 and are forced topass through discharge conduit 44. This discharge conduit is dividedinto two conduits 46 and 48.

The latter leads to product storage while the former serves torecirculate a portion of the distillation residuein the system. In orderto insure that the size of the solid distillation residue is kept belowa certain size it is passed through a screen 50, the oversize particlesbeing conducted by conduit 52 to product storage. The remaining portionof the distillation residue which passes through the screen 59 iscarried by conduit 54 to 'a hopper 56 from which it is fed by means of avariable screw feeder 58 into a preheating vessel B0. 7

Vessel 69 comprises two sections 62 and 3. The former and lower sectionserves to hold a bed of granular solids 66 upon a grid element 68 whilethe latter section serves as a disengaging space.

'To maintain bed 85 in fluidized condition, gas

containing oxygen such as air, is introduced through tube 70 at thebottom of the gas vessel 60. A cyclone 12 is provided for returning thesolid fines to the bed while the gaseous product escapes from the vesselthrough conduit M to 4 another cyclone EB where the separation of gasfrom solids is substantially completed. The gas is then led to purifyingapparatus through conduit 78.

Referring to Figures 2 and 3 of the drawings for detailed views of therotary retort H), numbers 80 and 82 designate cone-shaped end sectionsprovided with cylindrical flanges 84 and 86, respectively. The retort isrotatably supported at each end by rollers 88 and 90- which are mountedupon pedestals 92 and 93, respectively. Heavy flanges 94 and 95 areconnected l6 and i8 extend. A sealing device 185 is provided to seal offthe end of the retort. At the opposite end of the rotary retort acylindrical flange encloses an opening I08 through which the screwfeeder 28 disposed in conduit 21 extends. A sealing device H0 serves toseal this end of the retort from the atmosphere.

Within the retort in line with hopper 26 and directly opposed to oneanother are two lifters H2 and H4 (Figure 3). Each of these comprises arigid supporting member H6 which is sealed at one end to the inner wallof the cylindrical portion of the retort. This supporting member extendstoward the central longitudinal axis of the retort and is attached atits interior end to one edge of a scoop-like member H8, the other edgeof the member H8 being attached to the cone-shaped section 82. Thelifters are arranged so that their scoop portions are in line with thehopper 2B and are shaped in such a manner as to release their contentsinto the hopper as they traverse their paths above'the hopper.

In the preferred operation of my two vessel system as applied, forexample, to high volatile Pittsburgh seam coal which as previouslystated,

is a coking coal, the raw materials are finely divided coal and air withpossibly a small amount of steam. The retort Hl'is first charged withfinely divided previously distilled coal (preferably 0 to +4 mesh) whichhas been uniformly raised by suitable means to a distillationtemperature for starting purposes only. The temperature is preferably inthe range 800 to 1000 F. Finely divided previously distilled coal isalso charged to the preheating vessel 8i! and is raised to a temperaturesubstantially above that to be maintained in the retort and in generalis in the range 1000 to 1400 F. but may be less depending upon thetemperature to be maintained in-the retort. The heat required in thevessel 60 is preferably created by passing air or oxygen up through thebed of granular carbonaceous solids 68 whereby partial combustion takesplace and heat is evolved. This heat is immediately and uniformlyconducted throughout the entire bed.

The operation of the fluidization vessel to produce a fluidizedcondition is well known in the art. The velocity of the air, the depthof the bed, etc. are factors which can be readily determined. Because ofthe fluid condition of the bed, the granular solids therein containedare maintained at a uniform temperature. The gaseous products ofcombustion are separated from fines in the disengaging chamber 64 bymeans of a cyclone 12. Further separation is obtained by means ofcyclone 16. The gas so produced is a low E. t. u. gas useful for certainlimited purposes. If so desired. steam may be used in conjunction withthe air to produce a fluidized condition in the vessel 50. Thecomposition of the resulting gas is accordingly changed to some extent.While the use of a fluidized heating zone is preferred in practicing thepresent invention, other heating devices which are adapted to heatgranular solids uniformly throughout may be employed, for example,rabbled hearths or rotating kilns.

Hot distillation residue from vessel 60 is conducted to the retort, Iiithrough conduits l8 and i9 by means of the variable speed screw l8.Concurrently with the introduction of this residue a stream of finelydivided coal is introduced from hopper IQ. Both the coal and thedistillation residue are substantially within the same size range i. e.0 to +4 mesh. The two streams of solids are intimately mixed in theretort by in temperature with the" result' that distillation ofthecoalis rapid-and effective and the transition of the coal through the-plasti'c stage'to-a drystateis rapid. Little or no agglomeration ofthe-'coaltakes place;

The vaporous products are immediately withdrawn'from the upper-half oftheretort through.

the hopper 26 and out through conduitzl. Concurrently-with the removalof the vaporous prod ucts theabed of solidsin the rotating retort ismaintained at a substantially constant level by meansof lif-ters22- and24 which-pickup dry granular solids-from the opposite end oftheretort-a-ndidrop it into the hopper 26 This-continuous withdrawal ofgranularsolids results in: a continuous and progressive movement of thesolids from the inlet to the outlet end. The time within the retort'isadjusted by varying the'total input of solids into the retort as canIce-readily understood. For instance, ithas been found that with thepreheater at 1200F. and a distillation temperature of 90'0" F. in theretort, the time requiredto distill Pittsburgh seam coil, less than A--inch size, within the retort by the present process is from fifteen totwentyminutes.

The temperature maintained 'inthe retort is controlled by adjustingtherelative proportions of coal and granular distillation residueintroduced by the variable screw feeders l6 and It as well as byadjusting the temperature of the heated distillation residue before itsintroduction into the retort. If'desired; the coal charge canbepreheated up to a point just below that at which it begins'to give offhydrocarbon vaporsbeforebeing-ch'arged' to the retort. The temperaturedifferential between the distillation residue being fe d to the retortand the average distillation temperature within-the retort may be'asl'owas'50 F. In adjustingthe ratio of the proportion-of thePittsburghseamcoal to that 'of-"itsdistillation residue beingcharged tothe retort, to avoid agglomeration I havefound it neecssary to keep theratio: lessthan -l to 3 by weight.

Th'e vaporous products from the carbonizer are at least partially freedof'dust in the dust chamb'er -i'nthe conventional manner and from thereare" passedthrough a scrubber or condensing chambertdwhere the 'tarportion of the products is condensed out. The non-condensable portionwhich ishigh' B. t. u. gas'is removed fromthe top "through conduit4B,..to be further purifiedaccordingto the usual practices. 7

Theso'lid. products from the retort areforced by screw" 28 through the.discharge conduit 44 where. a portion thereof. is conducted toproductstorage through conduit. 45. 'Ihesize ,.of the distillation residue.leaving theretortis in.v general substantially the same as that of thecoalintroduced which in itself is anoteworthy discovery as respectsstrongly coking coal. since this solid prod: uct can .be-recirculatedfor usewithout further treatment and consequent loss of heat. However,occasionally a small percentage of the charmay beeabove the sizedesired. This larger size is screened-out on screen and conducted to theproduct storage through conduit 52. That-part which passesthrough'screen '50 .is carriedby-conduitM-orby any suitable means suchas an elevator; screw feeder, pneumatic means, etc. to the hopper 56from which it is fed to the fluidized vessel 60 by variable screw feeder58. The rate of feed of the solids will depend, of course'uponthe bed"level desired "in tl'ie lower section BZ-i'of the vessel-. Theabovecycle-isthenrepeated;

The products from the retort are carbonaceous: distillation residue,gas, tar, and water vapor. The product from the fluidized preheaterds avent gas.

The solidproduct produced as-the result of-' the applicationof'myprocess and apparatus to high volatile Pittsburgh seam coal asdescribed above; is a loose granular solid within substantially the samesize range as the coal charged to the process. It .is friable, cellularand non-agglomerated'in: contrast to that produced: by other methodsfromcoking coals. If properly controlled, as has beendscrib'ed-{with respectto the ratio of 'preheated material and coking coal charged, theproductis substantially free-of lumps of coke. Since a. large part" of thissolidproduct has: passed through the preheating zone, this part hasalower volatile content than that part which haspassed onl-ythrough theretort. The volatile content-or the: latter part is determined bytheaveragetemperature within the retort. The difference in volatile contentdepends on the temperature dif'-'-' ference between the preheating zoneand the;distill'ation zone and may accordingly be varied if desired. Thesolid product is suitable for use as solid boiler fuel as welI as formany other applications.

The-tar product is a fluid and by theabove process in the case of'thePittsburgh seamcoal; a yield of 26'to 27 gallons per ton of coal isobtained; Its ash content is less than 1% and when distilled up to300"-'C. 30% is found to pass over as distillate. Of this distillateapproximately 40% represents tar acids.

The gas from the-retort when separated from the condensable-portion hasapproximatelykBOO" B. t'. u. or more per cu. ft; The-yield of suchgas-is approximately 2000 cu. ft. per ton of'coal. The gaseous productfrom the'fluidized-preheater'hasa-B. t. u; content of 75'to and is at atemperature corresponding to that 'of-the"fluid izing vessel. About28,000 cu. ft. of this: gas is produced per tonof coal processed.

While the above example described the application of my invention tohigh volatile Pittsburgh seam coal, it was for purposes ofillustration1only'. The process andv apparatus hereinbeforedescribedmaybe applied to any distillable carbonaceous solids including" bothcoking and non-cokingbituminous coal,: lignites,- oil shales, and thelike: In thegapplication. to coking coals other: than: high volatilePittsburgh seam coal and: other: than coking 'oilshales, thezpreferredproportions of coal: or shale and, distillation residue-'charged"to the:retort may be othersthan those specified in the above example-dependingon: the particularcoking qualities: of the, coal but these maybe-readily" deter-mined. In:.the application to non-cokingcoals,lignites; andnon-coking oil shalesgreater latitude'in theadjustment ofthe proportions of fresh charge and hot distillation. residue and alsoin the selection of the operation temperatures is permitted, since thesematerials donot agglomerate. IHQSllCh cases the temperature to which.the chargeis heated and. the temperature ofthe-preheating zone-may be ashigh as it'is practical in order to accomplish the desired distillation.1

According to the provisions of the patent statutes, I have explained theprinciple} preferred construction, and mode of'operationof my inventionand have illustrated and described what I now consider to representitsbest-em- 7 bodiment. However, I desire to have it understood that,within the scope of the appended claims, the invention may be practicedotherwise than as specifically illustrated and described.

Iclaim:

1. In the method of distilling high volatile Pittsburgh seam coal bycontacting said coal directly with hot distillation residue frompreviously distilled coal in a closed unobstructed substantiallycylindrical horizontal retort which is mounted for rotation about itslongitudinal central axis, the steps comprising maintaining a granularbed consisting of said distillation residue in said retort in directcontact with the walls of said retort to serve as a barrier betweenfresh coal and said retort walls, rotating said retort, whereby a rotarymovement is imparted to said bed, continuously and separately feeding astream of said coal in finely divided form and a stream of hot finelydivided distillation residue into one end of said retort onto the top ofsaid bed, the mixing of said fresh coal and said hot residue beingeffected solely by the aforesaid rotary movement of said bed, said hotdistillation residue being at a temperature between 1000 and 14:00 F.and in such quantity that the average tem perature of the total solidsin the retort is between 800 and 1000 F., the ratio by weight of coaland distillation residue fed to said retort being less than 1 to 3,distilling the coal by heat supplied from the distillation residue,removing the volatile products from the retort, withdrawing distillationresidue from the retort in excess of that required to provide theaforesaid bed of distillation residue in said retort, conducting atleast a portion of said withdrawn residue to a preheating zone,circulating a gas containing oxygen gas under fluidizing conditionsthrough said portion in said preheating zone, oxidizing a portion of thesolids in the fluidized preheating zone to maintain a temperature insaid zone between 1000 and 1400 R, and returning said heated residue tothe retort to repeat the above cycle.

2. In the method of distilling high volatile Pittsburgh seam coal bycontacting said coal directly with hot distillation residue frompreviously distilled coal in a closed unobstructed substantiallycylindrical horizontal retort which is mounted for rotation about itslongitudinal central axis, the steps comprising maintaining a granularbed consisting of said distillation residue in said retort in directcontact with the walls of said retort to serve as a barrier betweenfresh coal and said retort walls, rotating said retort, whereby a rotarymovement is imparted to said bed, continuously and separately feeding astream of said coal in finely divided form and hot finely divideddistillation residue into one end of said retort onto the top of saidbed, the mixing of said fresh coal and said hot residue being effectedsolely by the aforesaid rotary movement of said bed, said hotdistillation residue being at a temperature between 1000 and 1400 F. andin such quantity that the average temperature of the total solids in theretort is between 800 and 1000 F., the ratio by weight of coal anddistillation residue fed to said retort being less than 1 to 3,distilling the coal by heat supplied by the distillation residue,removing distillation residue from the retort in excess of that requiredto provide the aforesaid bed of distillation residue in said retort,removing the volatile products from the retort, and returning at least aportion of the distillation residue after heating it to theaforementioned temperature range of 1000 to 1400" F. to the retort torepeat the above cycle.

3. In the method of distilling a highly coking coal by contacting saidcoal directly with hot distillation residue from previously distilledcoal in a closed unobstructed substantially cylindrical horizontalretort which is mounted for rotation about its longitudinal centralaxis, the steps comprising maintaining a granular bed consisting of saiddistillation residue in said retort in direct contact with the walls ofsaid retort to serve as a barrier between fresh feed and said retortwalls, rotating the retort, whereby a rotary movement is imparted tosaid bed, continuously and separately feeding a stream of said coal infinely divided form and a stream of hot finely divided distillationresidue into one end of said retort onto the top of said bed, the mixingof said fresh coal and said hot residue being effected solely by theaforesaid rotary movement of said bed, said hot distillation residuebeing at such a temperature and in such quantity that the averagetemperature of the total solids in the retort is at a distillationtemperature of said coal, the ratio by weight of coal and distillationresidue fed to said retort being less than 1 to 3, distilling the coalby the sensible heat supplied by the distillation residue, continuouslyremoving solid distillation residue from the opposite end of the retortin excess of that required to maintain the aforesaid bed of distillationresidue in said retort, removing the volatile products from the retort,continuously circulating at least a portion of the distillation residueto a combustion zone, circulating a gas containing oxygen gas underfiuidizing conditions through a bed of said distillation residue,oxidizing a portion of said solids in said fluidzed bed whereby theentire bed is maintained at a temperature substantialyl higher than thatrequired to effect distillation of said fresh coal, continuouslywithdrawing a portion of the hot solids from the fluidized bed, andrecycling it to the retort as said hot distillation residue.

4. In the method of distilling highly coking coal by contacting saidcoal directly with hot distillation residue from previously distilledcarbonaceous solids in a closed unobstructed substantially cylindricalhorizontal retort which is mounted for rotation about its longitudinalcentral axis, the steps comprising maintaining a granular bed consistingof said distillation residue in said retort in direct contact With thewalls of said retort to serve as a barrier between fresh feed and saidretort Walls, rotating the retort, whereby a rotary movement'is impartedto said bed, continuously and separately feeding a stream of said coalin finely divided form and a stream of hot finely divided distillationresidue into one end of said retort onto the top of said bed, the mixingof said fresh coal and said hot residue bein eifected solely by theaforesaid rotary movement of said bed, said hot distillation residuebein at such a temperature and in such quantity that the averagetemperature of the total solids in the retort is at a distillationtemperature of said coal, the ratio by Weight of coal and distillationresidue fed to said retort being less than 1 to 3, distilling the coalsolely by the sensible heat supplied by the distillation residue,continuously removing solid distillation residue from the opposite endof the retort in excess of that required to maintain the aforesaid bedof distillation residue in said retort, removing the volatile productsfrom the retort, and continuously returning at least a portion of thedistillation residue after heating it to an elevated Number Name Datetemperature to the retort to repeat the above 1,704,956 Trumble Mar. 12,1929 cycle. 1,775,323 Runge Sept. 9, 1930 CARL E. LESHER. 1,899,887Thiele Feb. 28 1933 5 1,983,943 Odell Dec. 11, 1934 REFERENCES CITED2,080,946 Lesher May 18, 1937 The following references are of record inthe 2,287,437 Lesher June 1942 file of this patent; 2,441,386 e g y 19482,455,327 Keith July 30, 1948 UNITED STATES PATENTS 10 2,462,366 DaviesFeb. 22, 1949 Number Name Date 2,480,670 Peck Aug. 30, 1949.

1,432,101 Danckwardt Oct. 17, 1922 1,433,039 Rodm-an Oct. 24, 1922 OTHER REFERENCES 1,664,723 Young Aim 3, 9 Flmdlzed Techmque, pages 261-266,Coke and 1,698,345 Puening Jan. 8, 1929 15 Gas, September 1947.

4. IN THE METHOD OF DISTILLING HIGHLY COKING COAL BY CONTACTING SAIDCOAL DIRECTLY WITH HOT DISTILLATION RESIDUE FROM PREVIOUSLY DISTILLEDCARBONACEOUS SOLIDS IN A CLOSED UNOBSTRUCTED SUBSTANTIALLY CYLINDRICALHORIZONTAL RETORT WHICH IS MOUNTED FOR ROTATION ABOUT ITS LONGITUDINALCENTRAL AXIS, THE STEPS COMPRISING MAINTAINING A GRANULAR BED CONSISTINGOF SAID DISTILLATION RESIDUE IN SAID RETORT IN DIRECT CONTACT WITH THEWALLS OF SAID RETORT TO SERVE AS A BARRIER BETWEEN FRESH FEED AND SAIDRETORT WALLS, ROTATING THE RETORT, WHEREBY A ROTARY MOVEMENT IS IMPARTEDTO SAID BED, CONTINUOUSLY AND SEPARATELY FEEDING A STREAM OF SAID COALIN FINELY DIVIDED FORM AND A STREAM OF HOT FINELY DIVIDED DISTILLATIONRESIDUE INTO ONE END OF SAID RETORT ONTO THE TOP OF SAID BED, THE MIXINGOF SAID FRESH COAL AND SAID HOT RESIDUE BEING EFFECTED SOLELY BY THEAFORESAID ROTARY MOVEMENT OF SAID BED, SAID HOT DISTILLATION RESIDUEBEING AT SUCH A TEMPERATURE AND IN SUCH QUANTITY THAT THE AVERAGETEMPERATURE OF THE TOTAL SOLIDS IN THE RETORT IS AT A DISTILLATIONTEMPERATURE OF SAID COAL, THE RATIO BY WEIGHT OF COAL AND DISTILLATIONRESIDUE FED TO SAID RETORT BEING LESS THAN 1 TO 3, DISTILLING THE COALSOLELY BY THE